1. Field of the Invention
The present invention relates to a method and an apparatus for controlling an internal combustion engine in which an air-fuel ratio of an air-fuel mixture is feedback controlled with elevated precision and high response speed to have an air-fuel ratio value which provides the best fuel cosumption.
2. Description of the Prior Art
An apparatus for optimum control of internal combustion engines is known in which the amount of intake air, which is a controlled variable of the internal combustion engine, is changed by a predetermined amount and the resultant change of the operating condition of the internal combustion engine is used to determine the direction of improvement of fuel consumption and the air-fuel ratio is modified in such a direction. The prior art apparatuses of this type are disclosed in the Laid-Open Japanese Patent Application Nos. 60639/80 and 49428/79 and U.S. Pat. No. 4026251.
In the conventional apparatuses, however, the period during which an internal combustion engine is operated with a controlled variable changed by a predetermined amount is not always an optimum period for the operating conditions of the engine, with the result that the accuracy of determining the direction of improvement of fuel consumption is not necessarily reliable. Therefore, it is difficult to feedback control the controlled variable of the internal combustion engine toward a controlled variable value for the best fuel consumption, which causes a loss of fuel consumption.
The present invention has been made to solve the above-mentioned problem.